Tree Roots 101

Things you might not know about roots


Roots can drown?

Common thinking is that tree roots can live without air since they are already underground. However, 25-percent of soil volume is typically air, 25-percent water, and 50-percent solid. Roots need this air space for "breathing." Burying existing root systems with extra soil can suffocate them. Some species of trees are very sensitive to having any soil fill placed over their root system. Don't risk damaging your trees with soil fill -- haul away extra soil instead of spreading it beneath existing trees!

Soil Volume

How deep are tree roots?

Roots on most trees are in the top 18 to 24 inches of the soil, not nearly as deep as everyone thinks. Severing roots with trenching activities and other excavations can fatally injure a tree. Often times the worst thing that can happen to a mature tree is for a deep trench (gas line or other utility line) to be dug inside the drip line (between the branch tips and the trunk).

It’s almost as if a tree is “sitting on a dime” when seeing its shallow roots.

It’s almost as if a tree is “sitting on a dime” when seeing its shallow roots.

Removing a large part of the root system can make a tree unstable, and reduce its ability to get nutrients and water from the soil. Open wounds on roots also creates an avenue for destructive pathogens, which may already be present in the soil, to enter the tree. While it is not recommended for branch cuts to be painted any more, it is recommended for large roots to be painted with a tree wound dressing.

BEFORE you begin new construction

Before you start construction on your building lot, select the trees you would like to keep. Some trees will have to be removed to allow for construction of the house and driveway. A professional nurseryman or arborist can help you identify the best trees to keep from the remaining group. Generally speaking, the Maples and Oaks will hold more value than weed trees like Black Locust and Wild Cherry. However, any tree in good condition in the right spot may be worth preserving.

To preserve the trees you decide to keep, follow these 3 steps:

1. Dig trenches for utility lines far away from important trees, beyond their driplines.
2. No excavating equipment or heavy trucks should be driven over top of roots (most tree roots are located from the trunk to just beyond the branch tips). Fence this area off with temporary fencing. Following this advice will also protect tree trunks from 'nicks' caused by excavation equipment like you see in the photo below.
3. Don't change the soil grade around trees by raising or lowering the soil level, or dump soil against tree trunks.


Ouch! Tree bark damaged by a skid steer loader.
Gag! Roots buried with excess soil fill.

Sidewalks damaged by tree roots

Trees are often planted in narrow lawn strips between streets and a sidewalks. The first sign of trouble is when concrete sidewalk slabs start to heave and crack, creating hazardous tripping spots for pedestrians.

Proper species selection will help curb this problem (pun intended) as well as the use of commercial root barriers, which act to deflect roots deeper into the ground, away from pavement. Root barriers need to be installed when a tree is first planted.


Tree roots heaved this concrete sidewalk and
created a hazardous situation.

Sidewalk and driveway damage from tree roots

Tree roots damage sidewalks and driveways due to the lifting and cracking of pavement while surface rooted trees will cause a bumpy lawn surface and compete with grass for water and nutrients.


Straightening a snow damaged tree

Cutting-off broken tree branches

Trimming damaged Japanese Maples